Vibrators of this type are known applicant's U.S. Pat. No. 4,356,736, Franz Riedl, issued Nov. 2, 1982.
Although with the known vibrator the frequency of the excited' oscillation can be varied by changing the speed of the drive motor and the direction of the vector of the directed vibration by shifting the pin relative to the hub groove, the m.r value is prescribed as a constant. It is frequently desired to be able to operate not only with a selectable, prescribed vibration frequency and a selectable, prescribed vibration direction, but also with a selectable, prescribed displacement of the vibration, at least between two different values, of the compaction element that is connected to the vibrator. The displacement "s" of the vibration is a function of the mass M of the compaction element and the mr value of the vibrator pursuant to the equation ##EQU1## where "m" is the vibrationally effective mass of the exciter and "r" is the distance of the center of gravity of this mass from the central axis of the unbalanced shaft.
It is an object of the present invention to provide a vibrator of the aforementioned general type where also the m.r value can be varied between a predetermined minimum value and a predetermined maximum value.